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Sedna
90377 Sedna is a large trans-Neptunian object, which as of 2012 was about three times as far from the Sun as Neptune. Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and nitrogen ices with tholins. Its surface is one of the reddest in the Solar System. It is probably a dwarf planet. History For most of its orbit it is even farther from the Sun than at present, with its aphelion estimated at 937 astronomical units[3] (31 times Neptune's distance), making it one of the most distant known objects in the Solar System other than long-period comets.[c][d] Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led to much speculation as to its origin. The Minor Planet Center currently places Sedna at the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, as Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud. Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster (an open cluster), or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a large planet beyond the orbit of Neptune. Astronomer Michael E. Brown, co-discoverer of Sedna and the dwarf planets Eris, Haumea, and Makemake, believes it to be the most scientifically important trans-Neptunian object found to date, as understanding its unusual orbit is likely to yield valuable information about the origin and early evolution of the Solar System.[12] Discovered Sedna (provisionally designated 2003 VB12) was discovered by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. The discovery formed part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yale's 160 megapixel Palomar Quest camera. On that day, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, which indicated that its distance was about 100 AU. Follow-up observations in November–December 2003 with the SMARTS telescope at Cerro Tololo Inter-American Observatory in Chile as well as with the Tenagra IV telescope at the W. M. Keck Observatory in Hawaii revealed that the object was moving along a distant highly eccentric orbit. Later the object was identified on older precovery images made by the Samuel Oschin telescope as well as on images from the Near Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a more precise calculation of its orbit.[13] "Our newly discovered object is the coldest most distant place known in the Solar System," said Mike Brown on his website, "so we feel it is appropriate to name it in honor of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean."[14] Brown also suggested to the International Astronomical Union's (IAU) Minor Planet Center that any future objects discovered in Sedna's orbital region should also be named after entities in arctic mythologies.[14] The team made the name "Sedna" public before the object had been officially numbered.[15] Brian Marsden, the head of the Minor Planet Center, said that such an action was a violation of protocol, and that some members of the IAU might vote against it.[16] However, no objection was raised to the name, and no competing names were suggested. The IAU's Committee on Small Body Nomenclature formally accepted the name in September 2004,[17] and also considered that, in similar cases of extraordinary interest, it might in the future allow names to be announced before they were officially numbered.[15] More Info Sedna has the longest orbital period of any known large object in the Solar System,[d] calculated at around 11,400 years.[3][a] Its orbit is extremely eccentric, with an aphelion estimated at 937 AU[3]and a perihelion at about 76 AU, the most distant perihelion ever observed for any Solar System object.[18] At its discovery it was 89.6 AU[19] from the Sun approaching perihelion, and was the most distant object in the Solar System yet observed. Eris was later detected by the same survey at 97 AU. Although the orbits of some long-period comets extend farther than that of Sedna, they are too dim to be discovered except when approaching perihelion in the inner Solar System. Even as Sedna nears its perihelion in mid 2076,[10][e] the Sun would appear merely as a very bright star in its sky, only 100 times brighter than a full Moon on Earth, and too far away to be visible as a disc to the naked eye.[20] When first discovered, Sedna was thought to have an unusually long rotational period (20 to 50 days).[20] It was initially speculated that Sedna's rotation was slowed by the gravitational pull of a large binary companion, similar to Pluto's moon Charon.[14] A search for such a satellite by the Hubble Space Telescope in March 2004 found nothing,[21][f] and subsequent measurements from the MMTtelescope suggest a much shorter rotation period of about 10 hours; rather typical for a body of its size.[23] Sedna.jpg Category:Dwarf Planets Category:Planets